Ferromagnetism in a new manganese-related Brownmillerite: La0.5Sr0.5MnO2.5.

The topotactic reduction of La0.5Sr0.5MnO3 leads to ordering of the anionic vacancies in the La0.5Sr0.5MnO2.5 composition. The isolated material, which is isostructural with Sr2Fe2O5, crystallises in the brownmillerite structural type with unit cell parameters a=0.54117(3), b=1.67608(12), c=0.54004(3) nm and space group Ibm2. Its microstructural characterisation by means of electron diffraction and high-resolution electron microscopy suggests a complex microstructure arising from the coherent intergrowth of different brownmillerite-type domains that show short-range ordering at the A sub-lattice. The layer structure of La0.5Sr0.5MnO2.5 leads to a double magnetic behaviour where a ferromagnetic two-dimensional component is present.